A typical freight train includes one or more locomotives, a plurality of railcars and several trainlines. The trainlines include both pneumatic and electrical lines some of which run from the lead locomotive to the last rail vehicle in the train. One pneumatic trainline especially important to a freight train is the brake pipe. The brake pipe consists of a series of individual pipe lengths interconnected to each other. One pipe length secured to the underside of each railcar interconnects to another such pipe length via a flexible coupler situated between each railcar. The brake pipe supplies the pressurized air that is required by the brake control system to charge the reservoirs and operate the air brake equipment on each railcar in the freight train.
A train operator situated in the lead locomotive can manipulate a brake handle to apply and release the brakes on the railcars as desired. The brake handle can be moved from and in between a release position at one extreme in which brake pipe pressure is maximum and the brakes are completely released to an emergency position at another extreme in which brake pipe pressure is zero and the brakes are fully applied. The brake handle positions include brake release, minimum service brake application, full service brake application and emergency brake application.
The brake control system on a freight train is ultimately controlled from the lead locomotive through a master controller. The inputs from the brake handle are typically processed by a cab unit and then passed to the master controller. Also referred to as the head end unit (HEU), the master controller operates according to instructions contained within its programming code. In response to these and other inputs, the master controller formulates a brake command appropriate to current conditions and issues it to each of the vehicles in the train. The HEU can order through the brake command any action from a release of brakes to an emergency application of brakes or any degree of brake application in between those two extremes. The precise degree of brake application ordered by the HEU is typically conveyed in terms of a percentage of the pressure required for full service brake application. Zero percent (0%) is typically designated for a release of brakes, 15% for a minimum service brake application, 100% for a full service brake application and 120% for an emergency brake application.
On a freight train, the brake command is typically conveyed to each of the rail vehicles in the form of an electrical signal using a two wire electrical trainline. The electrical trainline is typically contained with a protective conduit. Similar to the brake pipe, the electrical trainline actually constitutes a series of individual conduits. One individual conduit secured to the underside of each vehicle interconnects to another such conduit via a connector between each rail vehicle.
The brake equipment on each railcar of a freight train includes one or more brake cylinders, various electropneumatic valves, an air reservoir and a car control unit (CCU). Each CCU has its own unique identification code that is used for reporting its information to the master controller. Each CCU interprets and acts upon the electrical signal and controls the pressure contained within its corresponding reservoir.
The CCU typically includes a transceiver unit controlled by a microprocessor. The transceiver unit is connected to the electrical trainline from which it receives the electrical signal that carries the brake command issued by the master controller. The transceiver unit converts the electrical signal into a form usable by the microprocessor. In a manner known in the brake control art, the microprocessor controls the electropneumatic valves through which pressurized air can be supplied to or exhausted from the brake cylinders on the railcar according to the dictates of the particular brake command received. For example, in response to a command to apply the brakes, the microprocessor controls the electropneumatic valves so as to supply pressurized air to the brake cylinders. The brake cylinders convert this pressure to mechanical force. The mechanical force is then transferred to the brakes so as to slow or stop the rotation of the wheels on the railcar as commanded. Assuming the brake command is successfully communicated throughout the train, the brakes of all the railcars in the train respond in generally the same manner.
The communications network on board a freight train is typically comprised of the master controller in the lead locomotive and the CCU on board each railcar as well as the communications channel through which they communicate. The HEU is responsible for most of the communication over the network. Specifically, the HEU sends the most recently formulated brake command at a predetermined rate (e.g., every second) to each of the railcars. Sequentially or according to other criteria, the HEU also includes in each brake command a status query addressed to one railcar to determine whether the selected CCU is attentive to the brake control system. When so queried, a selected CCU will respond to the interrogation by sending to the master controller a signal in acknowledgement of the query. The acknowledgement takes the form of the identification code. More typically, the acknowledgement will also be accompanied by information such as reservoir pressure, brake pipe pressure, brake cylinder pressure, battery voltage and whether the brakes on the railcar or one of its trucks are cut-in (enabled) or cut out (disabled). By its response, the selected CCU informs the HEU that it is a properly operating part of the communications network. A CCU may also broadcast an exception message on the network should any of the following conditions occur: improper brake cylinder pressure, reservoir fails to charge, pressure in brake pipe or reservoir less than 50 psi or loss of communications. Specific control messages may also be issued by the CCU in response to certain circumstances as is well known in the brake control art.
The American Association of Railroads (AAR) has issued a specification entitled "Performance Requirement For Testing Electrically Controlled Pneumatic (ECP) Freight Brake Systems," Revision Number 8, dated Aug. 5, 1996. It is incorporated into this document by reference. The AAR specification defines how an ECP brake control system should respond to certain faults in communication over the communications network of a freight train. The AAR Document provides, for example, that should a fault occur that prevents the master controller from issuing brake commands to the CCUs, the CCUs shall self authorize each other to apply the brakes on the railcars. Specifically, the CCUs communicate with each other to determine how many of the CCUs are cutoff from the master controller. Operating according to directions contained in its programming code, each CCU orders an emergency application of brakes on its railcar if it has been collectively determined that a critical number of CCUs are cutoff from the master controller.
Section 3.3.2.2.2 of the AAR specification indicates that a CCU is programmed to release the brakes on its railcar should the CCU be unable to communicate with any other vehicle in the freight train. This prevents the affected railcar from applying its brakes (and damaging its wheels via sliding on the tracks) while the train continues to its destination. When the uncommunicative CCU fails to respond to the status query directed to it by the HEU, the HEU not only warns the train operator that the queried CCU failed to respond but also apprises the operator of the location that the failed CCU occupies in the train. Similarly, should each CCU in a group of railcars be unable to communicate with any other vehicle, the brakes of each railcar in that group would release. Only when more than a predetermined percentage (e.g., 15%) of CCUs lose the ability to communicate will the HEU warn the train operator to apply the brakes. If the train operator fails to respond to the warning within a given time, the HEU will automatically impose a penalty brake application by which it orders each of the remaining communicative CCUs to fully apply the brakes. Through this control logic, the master controller prevents the train from operating without sufficient braking power under almost all conditions.
Section 3.3.2.2.2 of the AAR specification, however, appears not to address a worst case scenario in which every CCU on the train loses its ability to communicate. If a failure of such magnitude were to occur, the brakes on every railcar would release, leaving the HEU with only the brakes on the locomotives to stop the train. Though unlikely to occur, such a failure could happen if even only one of the CCUs fails in such a way as to continuously transmit over the communications network. Such aberrant transmission by one CCU would completely prevent the HEU from transmitting to the other CCUs that are operating properly. There may conceivably be other types of failures that could completely prevent communications over the communications network. It is therefore desirable to introduce an invention that would overcome the shortcomings of the freight train brake control system prescribed by the current AAR specification.
It should be noted that the foregoing background information is provided to assist the reader in understanding the present invention. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.